Enhanced terahertz conductivity in ultra-thin gold film deposited onto (3-mercaptopropyl) trimethoxysilane (MPTMS)-coated Si substrates

Abstract

Various material properties change considerably when material is thinned down to nanometer thicknesses. Accordingly, researchers have been trying to obtain homogeneous thin films with nanometer thickness but depositing homogeneous few nanometers thick gold film is challenging as it tends to form islands rather than homogenous film. Recently, studies have revealed that treating the substrate with an organic buffer, (3-mercaptopropyl) trimethoxysilane (MPTMS) enables deposition of ultra-thin gold film having thickness as low as 5 nm. Different aspects of MPTMS treatment for ultra-thin gold films like its effect on the structure and optical properties at visible wavelengths have been investigated. However, the effect of the MPTMS treatment on electrical conductivity of ultra-thin gold film at terahertz frequency remains unexplored. Here, we measure the complex conductivity of nanometer-thick gold films deposited onto an MPTMS-coated silicon substrate using terahertz time-domain spectroscopy. Following the MPTMS treatment of the substrate, the conductivity of the films was found to increase compared to those deposited onto uncoated substrate for gold films having the thickness less than 11 nm. We observed 5-fold enhancement in the conductivity for a 7 nm-thick gold film. We also demonstrate the fabrication of nanoslot-antenna arrays in 8.2-nm-thick gold films. The nanoslot-antenna with MPTMS coating has resonance at around 0.5 THz with an electric field enhancement of 44, whereas the nanoslot-antenna without MPTMS coating does not show resonant properties. Our results demonstrate that gold films deposited onto MPTMS-coated silicon substrates are promising advanced materials for fabricating ultra-thin terahertz plasmonic devices.

ITO/Au/ITO multilayer thin films on transparent polycarbonate with enhanced EMI shielding properties

“…Au deposition is challenging due to its tendency to form islands instead of a continuous film. It is previously reported that the gold particles form disconnected island due to their surface diffusion in the early stages of the gold deposition by different fabrication methods [17]. The sizes of islands increase and then they coalesce to form a network by continued deposition.…”

“…Regarding to the quality of a thin metal interlayer between dielectric components, the fabrication process generally gives rise to aggregated gold islands before a homogeneous layer is deposited [17]. Sytchkova et al [18] and Guske et al [19] both reported that the thickness of metal film should exceed 10 nm to prevent discontinuity of the interlayer coat.…”

Extremely Thin Perfect Absorber by Generalized Multipole Bianisotropic Effect

“…Here, the disk is modeled as gold with a conductivity of σ = 2 × 10 6 Sm ‐1 , which is over one order of magnitude lower than its bulk value, given its few‐nanometer thickness. [ 46 ] Because of the conductive layer, the electric field at the top surface of the cylinder is partially screened, leading to a significantly damped resonance at 0.61 THz, as shown in Figure 1f. In this case, the field of the first mode near 0.6 THz changes from an ellipse‐like shape to a cone‐like shape, and the zero electric field plane of the second mode near 0.61 THz shifts lower, as shown in Figure 1f.…”

Colloidal MoS2 van der Waals Template for Growing Highly Uniform Nanomaterials

“…For the THz transmission measurement, high-resistivity Si (∼1000 Ω cm) was used for the reference substrates, with the thin MWCNTs samples drop-cast onto them. Additionally, we calculated the complex refractive index in the frequency domain using the relationship between the THz transmission field and the refractive indices . According to the extracted indices, the complex conductivity of the thin MWCNT samples was described using the following equation: where ε ∞ represents the relative permittivity at a high frequency, ε 0 represents the permittivity of free space, and σ­(ω) represents the complex conductivity .…”

“…Additionally, we calculated the complex refractive index in the frequency domain using the relationship between the THz transmission field and the refractive indices. 56 According to the extracted indices, the complex conductivity of the thin MWCNT samples was described using the following equation:…”